FIGS. 10 and 11 depict a conventional fuel supplying apparatus and a conventional pressure regulator shown in, for instance, Japanese Utility Model Application Laid-Open No. 6470/1989. As seen in FIG. 10, a pressure regulator 101' is installed in the engine compartment of a vehicle. A check valve 104' is disposed in a discharge port of a fuel pump 103' that is positioned in a fuel tank 102' containing fuel 108'. A pressure regulation passage 105' is provided through which the fuel discharged from' the fuel pump 103' flows, the fuel being subjected to pressure regulation by the pressure regulator 101'. An injector 106' is disposed in the pressure regulation passage 105' for supplying fuel to the engine. Excess fuel is returned to the fuel tank 102' by way of a return passage 107'.
As Seen in the cross-sectional view of FIG. 11, the pressure regulator 101' includes a case 1' and a fuel inlet port 2' which is an inlet port for pressurized fuel supplied from the fuel pump 103'. An excess-fuel passage 3' is used as a fuel outlet port for returning excess fuel during pressure regulation back to the fuel tank 102'. The regulator 101' also includes a cover 4', a pressure regulating spring 5' disposed in the cover 4', a diaphragm 6', a diaphragm support 7', and a spring seat 8' for clamping the diaphragm 6' together with the diaphragm support 7'. A valve portion 9' has a spherically shaped proximal portion that is fitted in the diaphragm support 7', and a valve seat 10' is adapted to perform a known valving operation as the valve portion 9' is brought into contact therewith during pressure regulation.
The conventional fuel supplying apparatus and pressure regulator are arranged as described above. The fuel 108' which is sucked and pressurized by the fuel pump 103' pushes open the check valve 104', passes through the pressure regulation passage 105', and is supplied from the fuel inlet port 2' of the pressure regulator 101' into the case 1'. When the pressure of the fuel within the case 1' reaches a pressure level which can be controlled by the pressure regulating spring 5', the diaphragm support 7' is pushed upward in cooperation with the flexibility of the diaphragm 6' against the pressure regulating spring 5'. Accordingly, the valve portion 9' is moved away from the valve seat 10', opens the excess fuel passage 3', and allows excess fuel to return to the fuel tank 102', thereby effecting the pressure regulation of the pressure regulation passage 105'.
The pressure regulator 101' of this type must be disposed downstream of the injector 106' in the pressure regulation passage 105', and the passage shutting-off performance of the valve portion 9' must be increased to secure a pressure maintaining function. For this reason, the proximal part of the valve portion 9' is formed by a ball to improve the shutting performance between the valve portion 9' and the valve seat 10'. Accordingly, even if the fuel pressurized by the fuel pump 103' is stopped, the passage is shut off by the pressure regulator 101' and the check valve 104', and the pressure within the pressure regulation passage 105' is maintained.
With the above-described conventional fuel supplying apparatus and pressure regulator, the pressure regulator 101' is disposed at a position within the engine compartment where the temperature becomes high, and the excess fuel Which has been pressure-regulated by the pressure regulator 101' returns through the return passage 107' to the fuel tank 102' via a high-temperature section. This has caused problems with respect to increased fuel temperature and the generation of large amounts of bubbles, thereby causing a decline in the efficiency of the fuel pump.
In addition, the pressure regulator 101' must be disposed downstream of the injector 106' in the pressure regulation passage 105', thereby requiring long metal piping for returning the excess fuel from the pressure regulator 101' to the fuel tank 102'.
Furthermore, when the engine is stopped and the supply of fuel from the fuel pump is stopped, the valve portion must possess good shutting performance characteristics to maintain pressure. This complicates the structure of the pressure regulator 101' so that the pressure regulator 101' cannot be made compact.